The present invention relates to a magnetic recording medium such as a magnetic disc and the like for use in magnetic disc devices, and a manufacturing method for the same.
In recent years, in the field of magnetic recording, particularly with respect to magnetic discs, remarkable improvements in the recording density have been achieved. In particular, recent improvements in the recording density have continued at a phenomenal pace, achieving rates of approximately 100 times in 10 years. Technologies supporting the improvement of recording density vary widely, however, one of the key concepts that can be mentioned is the technology of controlling the sliding characteristics between the magnetic head and magnetic recording medium.
Sliding of the head on the medium is unavoidable ever since the introduction of the CSS (Contactxe2x80x94Startxe2x80x94Stop) mode which is so-called xe2x80x9cWinchester formatxe2x80x9d as the main mode for hard disc drives, wherein the basic operation comprises the steps of sliding into contact, head flotation, and sliding into contact between the magnetic head and magnetic recording medium. Accordingly, problems relating to tribology between head and medium have become critical technical problems. Thus, properties such as resistance to abrasion and resistance to sliding over the surface of the magnetic recording medium comprise the keys to a reliable product, and efforts continue to develop and improve the protective film, lubricating film, and the like, which coat the magnetic film.
As a protective film for magnetic recording medium, films comprising various materials have been proposed. However, from the perspective of the total performance such as coating performance and durability, carbon films are principally employed.
These carbon films are generally formed according to a spatter-coating method, in which the coating conditions are extremely important due to their direct impact on resistance to corrosion and CSS properties.
In addition, in order to improve the recording density, it is preferable to reduce the flying height of the head, to increase the number of rotations of the medium, and the like. Thus, a superior resistance to sliding is required for the magnetic recording medium. On the other hand, in order to improve the recording density by means of reducing spacing loss, it""s preferable to make the protective film thinner, for example to a thickness of 100 xc3x85 or less. Hence, a thin, smooth and durable protective film is highly desired.
However, a carbon protective film formed according to the conventional spattering coating method, can sometimes lack durability, when the film is made thin, for example 100 xc3x85 or less.
Therefore, a plasma CVD method is currently being studied as a method for providing a carbon protective film with greater strength, compared to that produced by means of the spatter-coating method. This plasma CVD method is disclosed in, for example, Japanese Patent Application, Second Publication No. Hei 7-21858; First Publication Laid Open No. 7-73454; and the like.
However, under the current demands for increased recording density, it is difficult, from the perspective of durability to sliding, to produce a thin protective film to the point where a sufficiently high recording density is achieved without lowering the output properties, according to the aforementioned conventional technology. In addition, the conventional technology poses the problem of low coating rate, which in turn leads to production inefficiency.
In consideration of the aforementioned, the objectives of the present invention are described as follows.
(1) To provide a magnetic recording medium and manufacturing method thereof, that is reliable and capable of providing a sufficiently high recording density, without lowering the output properties.
(2) To provide a method for manufacturing the aforementioned magnetic recording medium in an efficient manner.
The method for manufacturing a magnetic recording medium according to the present invention comprises a method for manufacturing a magnetic recording medium by means of forming a carbon protective film onto the disc, the non-magnetic substrate of which is layered with a non-magnetic base film and magnetic film, using a reactant gas containing carbon atoms as a starting material, according to a plasma CVD method, wherein a mixed gas of hydrocarbon and hydrogen, in which the mixing ratio of hydrocarbon to hydrogen is in the range of 2 to 1xcx9c1 to 100 by volume, is used as a reactant gas, while applying a bias to said disc.
The aforementioned hydrocarbon preferably comprises at least one type of hydrocarbon selected from among lower saturated hydrocarbons, lower unsaturated hydrocarbons, and lower cyclic hydrocarbons, and more preferably comprises toluene.
In the case of using toluene, toluene and hydrogen are mixed, with a mixing ratio of toluene to hydrogen preferably in the range of 1 to 15xcx9c1 to 20 by volume.
The bias applied to the disc is preferably a high frequency bias.
In addition, formation of a carbon protective film is preferably carried out under high frequency electrical discharge.
When forming a carbon protective film on both sides of the disc at the same time, it is preferable to make the phases of electrical power supplied to each electrode arranged on the respective sides of the aforementioned disc different from each other. The phase difference of electrical power supplied to each electrode is preferably in the range of 90xcx9c270xc2x0, and in particular, more preferably the opposite phase (i.e., 180xc2x0).
The method for manufacturing a magnetic recording medium according to the present invention may comprise a method for manufacturing a magnetic recording medium by means of forming a carbon protective film onto the disc the non-magnetic substrate of which is layered with a non-magnetic base film and magnetic film, using a reactant gas containing carbon atoms as a starting material, according to a plasma CVD method, wherein pulse D.C. bias having a frequency of 1 kHzxcx9c100 GHz and pulse width of 1 nsxcx9c500 xcexcs is applied to the disc, when forming (during formation of) the carbon protective film.
The frequency of the pulse D.C. bias applied to the disc is preferably in the range of 10 kHzxcx9c1 GHz, and the pulse width is preferably in the range of 10 nsxcx9c50 xcexcs.
The average voltage of the pulse D.C. bias applied to the disc is preferably in the range of xe2x88x92400xcx9cxe2x88x9210V.
The aforementioned reactant gas is preferably a mixed gas of hydrocarbon and hydrogen, with a mixing ratio of hydrocarbon to hydrogen in the range of 2 to 1xcx9c1 to 100 by volume. The hydrocarbon preferably comprises at least one type of hydrocarbon selected from among lower saturated hydrocarbons, lower unsaturated hydrocarbons, and lower cyclic hydrocarbons.
The magnetic recording medium according to the present invention is provided with a carbon protective film onto the disc, the non-magnetic substrate of which is layered with a non-magnetic base film and magnetic film, that can be formed according to a plasma CVD method while applying pulse D.C. bias having a frequency of 1 kHzxcx9c100 GHz and pulse width of 1 ns 500 xcexcs to the disc.
The method for manufacturing a magnetic recording medium according to the present invention may comprise a method for manufacturing a magnetic recording medium by means of forming a carbon protective film onto the disc, the non-magnetic substrate of which is layered with a non-magnetic base film and magnetic film, using a reactant gas containing carbon atoms as a starting material, according to a plasma CVD method, wherein the temperature of the disc is heated to 100xcx9c250xc2x0 C. prior to forming the aforementioned carbon protective film.
The temperature of the disc is preferably in the range of 150xcx9c200xc2x0 C.
The aforementioned reactant gas is preferably a mixed gas of hydrocarbon and hydrogen, with a mixing ratio of hydrocarbon to hydrogen in the range of 2 to 1xcx9c1 to 100 by volume, wherein the hydrocarbon mixed into the reactant gas preferably comprises at least one type of hydrocarbon selected from among lower saturated hydrocarbons, lower unsaturated hydrocarbons, and lower cyclic hydrocarbons.
The pressure of the reactant gas is in the range of 0.1xcx9c10 Pa, and preferably 2xcx9c6 Pa, when forming the carbon protective film in the method for manufacturing a magnetic recording medium according to the present invention.
The aforementioned reactant gas is preferably a mixed gas of hydrocarbon and hydrogen, with a mixing ratio of hydrocarbon to hydrogen in the range of 2 to 1xcx9c1 to 100 by volume, wherein the hydrocarbon mixed into the reactant gas preferably comprises at least one type of hydrocarbon selected from among lower saturated hydrocarbons, lower unsaturated hydrocarbons, and lower cyclic hydrocarbons.
The method for manufacturing a magnetic recording medium according to the present invention may comprise a method for manufacturing a magnetic recording medium by means of forming a carbon protective film onto the disc, the non-magnetic substrate of which is layered with a non-magnetic base film and magnetic film, using a reactant gas containing carbon atoms as a starting material, according to a plasma CVD method, wherein the reactant gas is a mixed gas of hydrocarbon and hydrogen, with a mixing ratio of hydrocarbon to hydrogen in the range of 2 to 1xcx9c1 to 100 by volume, into which nitrogen gas is added at a adding volume of 0.1xcx9c100% of the mixed gas.
The aforementioned hydrocarbon preferably comprises at least one type of hydrocarbon selected from among lower saturated hydrocarbons, lower unsaturated hydrocarbons, and lower cyclic hydrocarbons.
The magnetic recording medium according to the present invention may comprise a non-magnetic substrate, layered with a non-magnetic base film, magnetic film, carbon protective film, and lubricating film, wherein said carbon protective film comprises a plasma CVD carbon layer formed according to a plasma CVD method, and a spatter carbon layer formed according to a spattering coating method, which lies in contact with the lubricating film.
The thickness of the spatter carbon layer is in the range of 5xcx9c100 xc3x85, and preferably 30xcx9c100 xc3x85, and the thickness of a plasma CVD carbon layer is preferably in the range of 30xcx9c100 xc3x85.
In addition, the method for manufacturing a magnetic recording medium may comprise the steps of forming (1) a plasma CVD carbon layer, using a reactant gas containing carbon atoms as a starting material, according to a plasma CVD method, (2) a spatter carbon layer thereon, using a spatter gas, according to a spatter-coating method, and (3) a lubricating film thereon, which lies in contact with said spatter carbon layer.
The reactant gas used for forming a plasma CVD carbon layer according to a plasma CVD method is preferably a mixed gas of hydrocarbon and hydrogen, with a mixing ratio of hydrocarbon to hydrogen in the range of 2 to 1xcx9c1 to 100 by volume, wherein the hydrocarbon preferably comprises at least one type of hydrocarbon selected from among lower saturated hydrocarbons, lower unsaturated hydrocarbons, and lower cyclic hydrocarbons.
The spatter gas used for forming a spatter carbon layer according to the spatter-coating method is preferably argon, into which at least one gas selected from among nitrogen, hydrogen, and methane, is added at a mixing ratio to the argon of 0.1xcx9c100% by volume.
In addition, the method for manufacturing a magnetic recording medium according to the present invention may comprise a method for manufacturing a magnetic recording medium by means of forming a carbon protective film on a disc, the non-magnetic substrate of which is layered with a non-magnetic base film and magnetic film, using a reactant gas containing carbon atoms as a starting material, according to a plasma CVD method, and lubricating film thereon, which lies in contact with the carbon protective film, wherein said films are formed while performing bias applying to the disc, with subsequent films formed without bias applying to the disc.
The bias applied to the disc is preferably a pulse D.C. bias of xe2x88x92400xcx9cxe2x88x9210V, or a high frequency bias of 10xcx9c300 W.
The thickness of the carbon layer which is formed without bias applying to the disc is preferably in the range of 5xcx9c20 xc3x85.
The aforementioned reactant gas is preferably a mixed gas of hydrocarbon and hydrogen, with a mixing ratio of hydrocarbon to hydrogen in the range of 2 to 1xcx9c1 to 100 by volume, wherein the hydrocarbon preferably comprises at least one type of hydrocarbon selected from among lower saturated hydrocarbons, lower unsaturated hydrocarbons, and lower cyclic hydrocarbons.
In addition, the magnetic recording medium according to the present invention may comprise a carbon protective film and a lubricating film on a disc, the non-magnetic substrate of which is layered with a non-magnetic base film and magnetic film, wherein the carbon protective film comprises a first carbon layer, that is formed according to a plasma CVD method while performing bias applying to the disc, and a second carbon layer, which lies in contact with the lubricating film, that is formed according to a plasma CVD) method without bias applying to the disc.
The thickness of the second carbon layer is preferably in the range of 5xcx9c20 xc3x85.
In addition, the magnetic recording medium according to the present invention may comprise a non-magnetic base film, magnetic film, protective film, and lubricating film on the non-magnetic substrate; wherein the protective film comprises a carbon layer, principally comprising carbon, on a tantalum nitrogen layer, comprising tantalum and nitrogen with a mixing ratio of nitrogen of 1xcx9c30% atm, with said carbon layer being formed according to a plasma CVD method, and lying in contact with the lubricating film.
The thickness of the carbon layer is preferably in the range of 5xcx9c100 xc3x85, while the thickness of the tantalum nitrogen layer is preferably 1xcx9c95 xc3x85.
The method for manufacturing a magnetic recording medium according to the present invention may comprise the steps of forming (1) a non-magnetic base film and magnetic film on a non-magnetic substrate; (2) a tantalum nitrogen layer thereon, which comprises a material containing nitrogen and tantalum, with a mixing ratio of nitrogen of 1xcx9c30% atm; (3) a carbon layer thereon, which is formed according to a plasma CVD method, using a reactant gas containing carbon atoms, and (4) a lubricating film thereon, which lies in contact with the carbon layer.
The aforementioned reactant gas is preferably a mixed gas of hydrocarbon and hydrogen with a mixing ratio of hydrocarbon to hydrogen in the range of 2 to 1xcx9c1 to 100 by volume. The hydrocarbon preferably comprises at least one type of hydrocarbon selected from among lower saturated hydrocarbons, lower unsaturated hydrocarbons, and lower cyclic hydrocarbons.
In addition, the method for manufacturing a magnetic recording medium according to the present invention may comprise a method for manufacturing a magnetic recording medium by means of forming (1) a non-magnetic base film and magnetic film, (2) a carbon film thereon, using a reactant gas containing carbon atoms as a starting material, according to a plasma CVD method, and subsequently (3) a lubricating film on the carbon protective film, wherein the surface of the carbon protective film is irradiated with ultraviolet rays before forming the lubricating film.
The wavelength of the ultraviolet rays irradiating the carbon protective film is preferably in the range of 100xcx9c400 nm, and the source of the ultraviolet rays is preferably an excimer emission lamp.
Additionally, the surface of the carbon protective film is preferably washed, using water, before forming the lubricating film thereon.
The aforementioned reactant gas preferably comprises a mixed gas of hydrocarbon and hydrogen, with a mixing ratio of hydrocarbon to hydrogen in the range of 2 to 1xcx9c1 to 100 by volume. The hydrocarbon preferably comprises at least one type of hydrocarbon selected from among lower saturated hydrocarbons, lower unsaturated hydrocarbons, and lower cyclic hydrocarbons.
In addition, the method for manufacturing a magnetic recording medium may comprise a method for manufacturing a magnetic recording medium by means of forming (1) a non-magnetic base film and magnetic film, (2) a carbon film thereon, using a reactant gas containing carbon atoms as a starting material, according to a plasma CVD method, and subsequently (3) a lubricating film on the carbon protective film; wherein the surface of the carbon protective film is washed, using water, before forming the lubricating film thereon.
When washing the carbon protective film, the cleaning water used preferably comprises water of a high purity.
In addition, the magnetic recording medium according to the present invention may comprise a non-magnetic base film, magnetic film, carbon protective film, and lubricating film on a non-magnetic substrate, wherein the carbon protective film is formed according to a plasma CVD method, followed by irradiation of the surface of the carbon protective film with ultraviolet rays.
Additionally, the magnetic recording medium according to the present invention may comprise a non-magnetic base film, magnetic film, carbon protective film, and lubricating film on a non-magnetic substrate, wherein the carbon protective film is formed, using a reactant gas containing carbon atoms as a starting material, according to a plasma CVD method, and the lubricating film principally comprises at least one chemical compound represented by the following formula (1) through (5), the number average molecular weights of which lie in the range of 500xcx9c6000. xe2x80x83Fxe2x80x94(CF2CF2CF2O)pxe2x80x94CF2CF2xe2x80x94COOCH2CH2xe2x80x94Oxe2x80x94C6H5xe2x80x83xe2x80x83(2)
Fxe2x80x94(CF2CF2CF2O)qxe2x80x94CF2CF2CH2xe2x80x94OHxe2x80x83xe2x80x83(3)
HOCH2xe2x80x94CF2Oxe2x80x94(C2F4O)rxe2x80x94(CF2O)sxe2x80x94CF2xe2x80x94CH2OHxe2x80x83xe2x80x83(4)
HOxe2x80x94(CH2CH2xe2x80x94O)txe2x80x94CH2CF2Oxe2x80x94(CF2CF2O)uxe2x80x94CF2O)vxe2x80x94CF2CH2xe2x80x94(OCH2CH2)vxe2x80x94OHxe2x80x83xe2x80x83(5)
[wherein, m, n, p, q, r, s, t, u, v, and w each represents an integer].
Additionally, the lubricating film may principally comprise a mixture, which is formed by means of adding a chemical compound represented by the following formula (6), into the aforementioned chemical compound, at a mixing ratio 0.1xcx9c20% by weight. 
[wherein, x represents an integer between 0 and 6].
Among the aforementioned, in particular, a lubricating film principally comprising a compound represented by the aforementioned formula (1) or (5), the number average molecular weights of which lie in the range of 500xcx9c6000, is preferred.
In addition, the aforementioned magnetic recording medium may comprise a non-magnetic base film, a magnetic film containing Co, and a carbon protective film formed according to a plasma CVD method, on a non-magnetic substrate, wherein the extraction amount of Co is no greater than 3 ng/cm2 with respect to the area of the substrate, and preferably no greater than 2 ng/cm2, and more preferably, no greater than 1.5 ng/cm2.
In addition, the method for manufacturing a magnetic recording medium according to the present invention may comprise a method for manufacturing a magnetic recording medium by means of forming (1) a non-magnetic base film and magnetic film on a non-magnetic substrate, and (2) a carbon protective film thereon, using a reactant gas containing carbon atoms as a starting material, according to a plasma CVD method, wherein the surface of the non-magnetic substrate is treated with texture-processing to form an average roughness (Ra) of the surface of the non-magnetic substrate is 1xcx9c20 xc3x85.
When texture-processing the surface of the non-magnetic substrate in the aforementioned manner, the average roughness of the surface is more preferably in the range of 3xcx9c10 xc3x85.
The method for texture-processing is preferably a mechanical method for texture-processing, in which abrasive particles are used, preferred examples of which may include processes in which the average particle diameter is 0.1xcx9c5 xcexcm.
The method for mechanical texture-processing is a method for treating the surface of the non-magnetic substrate with texture-processing, by means of rotating the non-magnetic substrate while At the same time running an abrasive tape over the substrate in contact with the surface of the non-magnetic substrate, and supplying abrasive particles between the abrasive tape and non-magnetic substrate. In this method, it is preferable to oscillate the abrasive tape in a direction which crosses the aforementioned running direction, at a frequency of 0.1xcx9c5 Hz.
The rotational speed of the non-magnetic substrate when performing texture-processing is preferably in the range of 300xcx9c2000 rpm.
The aforementioned reactant gas is preferably a mixed gas of hydrocarbon and hydrogen, wherein the hydrocarbon preferably comprises at least one type of hydrocarbon selected from among lower saturated hydrocarbons, lower unsaturated hydrocarbons, and lower cyclic hydrocarbons.
In addition, the magnetic recording medium according to the present invention may comprise a non-magnetic base film, magnetic film, and carbon protective film, which are formed on the non-magnetic substrate according to a plasma CVD method; wherein the average surface roughness (Ra) of the non-magnetic substrate is in the range of 1xcx9c20 xc3x85.
In addition, the method for manufacturing a magnetic recording medium according to the present invention is a method for manufacturing a magnetic recording medium by means of forming a carbon protective film on a disc, the non-magnetic substrate of which is layered with a non-magnetic base film and magnetic film, using a reactant gas containing carbon atoms as a starting material, according to a plasma CVD method, wherein bias applying is performed to the disc at the time of forming the carbon protective film, and the reactant gas is either butadiene gas or a mixed gas of butadiene and hydrogen comprising a mixing ratio of butadiene to hydrogen in the range of 100 to 0xcx9c1 to 100 by volume.
With regard to the aforementioned reactant gas, the mixing ratio of butadiene to hydrogen is preferably in the range of 100 to 0xcx9c1 to 25 by volume.
Additionally, the method for manufacturing a magnetic recording medium according to the present invention may comprise a method for manufacturing a magnetic recording medium by means of exposing a disc, in which both surfaces of the non-magnetic substrate are layered with a non-magnetic base film and magnetic film, to a reactant gas containing carbon atoms, while supplying electrical power to electrodes arranged on both sides of the disc to generate plasma, and form a carbon protective film on both sides of the disc, using the aforementioned reactant gas as a starting material, according to a plasma CVD method, wherein bias applying is performed to the disc at the time of forming the carbon protective film, the electrical power supplied to the aforementioned electrodes comprises high frequency electrical power; and the reactant gas comprises either butadiene gas or a mixed gas of butadiene and hydrogen, with a mixing ratio of butadiene to hydrogen in the range of 100 to 0xcx9c1 to 100 by volume.
When forming the carbon protective film, it is preferable to make the phases of electrical power supplied to each electrode arranged on both sides of the disc different from each other. The phase difference in the phase of electrical power supplied to each electrode is preferably in the range of 90xcx9c270xc2x0, and in particular, more preferably comprises the opposite phase (i.e., 180xc2x0).
The thickness of the carbon protective film is preferably in the range of 30xcx9c100 xc3x85.